The present invention relates to impact-resistant polyester injection-moulded parts and more particularly to injection-moulded parts based on a polyester (A) and on at least one copolymer (B) of ethylene and of an unsaturated epoxy, the copolymer (B) being obtained by copolymerization or grafting of the unsaturated epoxy.
The impact resistance of polyesters is generally improved by incorporating, in the form of a dispersed phase, an impact modifier which is elastomeric and has reactive functional groups (acrylic acid, maleic anhydride, etc.) capable of reacting with functional groups of the polyester matrix. This reactivity ensures fine and homogeneous dispersion of the elastomer and good adhesion at the nodule-matrix interface, but results in a significant drop in the melt flow. This appreciable change in the viscosity is detrimental to the processing, especially in the case of thin or large-sized injection-moulded parts.
The applicant has discovered that by using compositions based on polyester resin and on at least one copolymer of ethylene and of an unsaturated epoxy it was possible to obtain both impact resistance and good melt flow allowing injection moulding of these compositions, provided that the amounts of copolymers and the epoxy content of the copolymer are chosen.
The prior art has already described polyester-based impact-resistance compositions.
U.S. Pat. No. 4,172,859 describes polyesters modified by reactive copolymers in order to increase the impact resistance. The polyester matrix contains 0.01 to 3 micron nodules of reactive copolymer; the reactive copolymer must adhere partly to the matrix, its modulus is between 1 and 20,000 psi (0.007 and 138 MPa) and the ratio of the modulus of the matrix to the modulus of the reactive copolymer is greater than 10. The reactive copolymer may contain up to 50 mol % of glycidyl methacrylate.
No mention is made regarding the viscosity of the polyesters modified in this way. U.S. Pat. No. 4,753,890 describes polyesters such as, for example, polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), modified by ethylene/alkyl (meth)acrylate/glycidyl (meth)acrylate copolymers. Table 1 shows PET or PBT containing 18% of copolymer. It is considered that copolymers containing 2.25 to 8.6% by weight of glycidyl methacrylate (GMA) are suitable for the invention. No mention is made regarding the viscosity.
U.S. Pat. No. 5,208,292 describes PET compositions and PBT compositions modified by a blend of copolymers which crosslink. In that document a PBT is described which contains a blend of a copolymer having GMA units and of a copolymer having maleic inhydride units. It is emphasized that the incorporation of a blend thus crosslinked into the PBT makes it possible to avoid too great a drop in the melt flow index or MFI. Comparative Example 1 shows that a blend of 80 parts of PBT having an MFI of 79.3 (250xc2x0 C.; 5 kg) and of 20 parts of an ethylene/ethyl acrylate/GMA copolymer having an MFI of 11 (190xc2x0 C.; 2.16 kg) and containing 12% by weight of GMA resulted in a modified PBT having an MFI of 1.7 (250xc2x0 C.; 5 kg), making injection-moulded parts impossible.
Thus, the prior art has disclosed polyesters modified by GMA-containing copolymers but was not interested in the melt flow of the polyesters thus modified. Tests and measurements of the properties of these modified polyesters have been carried out on test pieces made by compression moulding or injection moulding.
It is clear that the viscosity is of no importance in the case of such dimensions and under laboratory conditions.
The situation is completely different in the case of thin or larger-sized parts, or those of a complicated shape, these parts having to be produced at industrial rates.
The advantage of the compositions of the invention is the compromise between impact resistance and viscosity.
U.S. Pat. No. 5,208,292 partly solves the problem of the drop in melt flow but at the cost of a blend of copolymers to be crosslinked, which requires having to correctly meter the products according to the amounts of reactive functional groups that they contain.
Another advantage of the invention is that it is necessary to add only a single product to the polyester resin, and not a blend of various products. Another advantage is that the ethylene/unsaturated epoxy copolymer is merely added into the extruder which feeds the injection-moulding machine. This addition may be carried out by a lateral extruder or a granule metering hopper on the polyester extruder. The blend of the polyester resin and of the impact modifier need therefore not be prepared in advance.
The Applicant has discovered that compositions such that weight % (B)xc3x97MFI (A+B)/MFI (A) is greater than 3 are perfectly suitable for making the impact-resistant injection-moulded parts of the present invention.
In this expression, MFI (A+B) denotes the melt flow index of the modified polyester, that is to say of the blend of (A) and (B) and any fillers such as glass fibres, fire retardants, antioxidants, etc, and MFI (A) denotes the melt flow index of the same compositions but not containing (B), that is to say MFI (A) denotes the melt flow index of the polyester by itself and of the polyester filled with glass fibres and any fire retardants and antioxidants, etc.
The present invention relates to polyester injection-moulded parts based on a polyester (A) and on an ethylene/unsaturated epoxy copolymer (B), such that the weight % (B)xc3x97MFI (A+B)/MFI (A) expression, in which:
MFI (A+B) denotes the melt flow index of the modified polyester, that is to say the blend of (A) and (B) and of any fillers;
MFI (A) denotes the melt flow index of the polyester (A) and of any fillers [without (B)]; and
weight % (B) denotes the weight percentage of (B) in the blend of (A) and (B) and of any fillers; is greater than 3.
The term xe2x80x9cpolyesterxe2x80x9d denotes polymers which are saturated products resulting from the condensation of glycols with dicarboxylic acids or their derivatives. Preferably, they comprise products resulting from condensation of aromatic dicarboxylic acids, having from 8 to 14 carbon atoms, with at least one glycol chosen from the group consisting of neopentyl glycol, cyclohexanedimethanol and aliphatic glycols of formula HO(CH2)nOH in which n is an integer ranging from 2 to 10. Up to 50 mol % of the aromatic dicarboxylic acid may be replaced with at least one other aromatic dicarboxylic acid having from 8 to 14 carbon atoms and/or up to 20 mol % may be replaced with an aliphatic dicarboxylic acid having from 2 to 12 carbon atoms.
The preferred polyesters are polyethylene terephthalate (PET), poly(1,4-butylene terephthalate) (PBT), 1,4-cyclohexylene dimethylene terephthalate(isophthalate) and other esters derived from aromatic dicarboxylic acids such as isophthalic acid, dibenzoic acid and naphthalene dicarboxylic acid, 4,4xe2x80x2-diphenylenedicarboxylic acid, bis(p-carboxyphenyl)methane, ethylene bis (p-benzoic) acid, 1-4-tetramethylene bis(p-oxybenzoic) acid, ethylene bis (para-oxybenzoic) acid, 1,3-trimethylene bis (p-oxybenzoic) acid, and glycols such as ethylene glycol, 1,3-trimethylene glycol, 1,4-tetramethylene glycol, 1,6-hexamethylene glycol, 1,3-propylene glycol, 1,8-octamethylene glycol and 1,10-decamethylene glycol. The MFI of these polyesters, measured at 250xc2x0 C. and with 2.16 kg, may vary from 2 to 100 and advantageously from 10 to 80.
The ethylene/unsaturated epoxy copolymer (B) may be obtained by copolymerizing ethylene with an unsaturated epoxy or by grafting the unsaturated epoxy onto polyethylene. The grafting may be carried out in a solvent phase or onto the polyethylene in the melt in the presence of a peroxide. These grafting techniques are known per se. As regards the copolymerization of ethylene with an unsaturated epoxy, processes called radical polymerization normally operating at pressures between 200 and 2500 bar may be used.
By way of example of unsaturated epoxies, mention may be made of:
aliphatic glycidyl esters and ethers, such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate and itaconate, glycidyl (meth)acrylate, and,
alicyclic glycidyl esters and ethers, such as 2-cyclohexen-1-yl-glycidyl ether, diglycidyl cyclohexene-4,5-dicarboxylate, glycidyl cyclohexene-4-carboxylate, glycidyl 2-methyl-5-norbornene-2-carboxylate and diglycidyl endo-cis-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate.
The ethylene/unsaturated epoxy copolymer may also comprise other monomers, these possibly being chosen, for example, from:
alpha-olefins, such as propylene, 1-butene, hexene, etc;
vinyl esters of saturated carboxylic acids, such as vinyl acetate or vinyl propionate;
esters of saturated carboxylic acids, such as alkyl (meth)acrylates, possibly having up to 24 carbon atoms.
By way of example, the unsaturated epoxy may be grafted onto the following polymers:
polyethylene, ethylene/alpha-olefin copolymers, polyethylenes such as VLDPE (very-low-density PE), ULDPE (ultra-low-density PE) or metallocene PE;
copolymers of ethylene with at least one vinyl ester of a saturated carboxylic acid, such as vinyl acetate or vinyl propionate;
copolymers of ethylene with at least one unsaturated carboxylic acid ester, such as alkyl (meth)acrylates, possibly having up to 24 carbon atoms;
EPR (ethylene-propylene rubber) elastomers or EPDM (ethylene-propylene-diene monomer);
blends of polymers chosen from the above.
The amount of copolymer (B) may vary over wide limits depending on the properties that are demanded of the blend of (A) and (B); however, amounts up to 25%, and advantageously between 10 and 20%, by weight of (A)+(B) are sufficient.
The Applicant has discovered that, for an identical epoxy content and by varying the amount of copolymer (B) from 10 to 20%, the gain obtained above 15% was much less than the gain obtained when going from 10 to 15%, while the melt flow index dropped significantly.
The Applicant has also discovered that, for a constant amount of copolymer (B), the impact strength was not strictly proportional to the amount of epoxy in the copolymer (B).
The applicant has found that, in order to satisfy the weight % (B)xc3x97MFI (A+B)/MFI (A) greater than 3 criterion, it was merely necessary to choose (B) so as to contain an amount of epoxy up to 5%, and preferably 1 to 3%, by weight.
Advantageously, the amount of (B) is 10 to 20% by weight of(B)+(A).
The copolymer (B) of the injection-moulded parts of the invention is advantageously an ethylene/alkyl (meth)acrylate/unsaturated epoxy copolymer.
Advantageously, it may contain up to 40% by weight of alkyl (meth)acrylate.
Advantageously, the epoxy is glycidyl (meth)acrylate.
Advantageously, the alkyl (meth)acrylate is chosen from methyl (meth)acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate.
The amount of alkyl (meth)acrylate is advantageously from 20 to 35%.
The MFI of (B) is advantageously between 2 and 40 and is preferably from 5 to 20 (190xc2x0 C.-2.16 kg).
This copolymer may be obtained by radical polymerization of the monomers.
The polyester (A) may contain glass fibre. The amount of glass fibre may be up to 35 parts for 65 parts of (A). Advantageously, amounts from 20 to 30 parts are used per 80 to 70 parts of (A), respectively.
According to another embodiment of the invention the copolymer (B) may consist of an ethylene/unsaturated epoxy copolymer (B1) as a blend with a polyolefin (C). The amount of epoxy in (B1) may have any value provided that the weight % (B1+C)xc3x97MFI (A+B1+C)/MFI (A) greater than 3 criterion is satisfied.
(B1) may be chosen from the same polymers mentioned in the case of (B) and preferably ethylene/alkyl (meth)acrylate/unsaturated epoxy copolymers.
The amount of epoxy in (B1) may be greater than that in (B), for example up to 10% by weight. This is in fact a dilution of (B1) by (C). The amount of epoxy weight % in (B1)+(C) is in the same proportions as that in (B).
The polyolefin (C) may be chosen from the polymers mentioned above, on which polymers an unsaturated epoxy may have been grafted.
Preferably, (C) is an ethylene/alkyl (meth)acrylate copolymer. The alkyl (meth)acrylate may be chosen from those mentioned above in the description of (B). The MFI of (C) is advantageously between 2 and 40 and preferably is from 5 to 20 (190xc2x0 C.-2.16 kg). The proportions of (B1) and (C) depend on the amount of epoxy in (B1). By way of example, and in the case of amounts of epoxy of about 5 to 8% by weight of (B1), the proportions of (B1) to (C) are in the ratios from 12/8 to 8/12, or from 40/60 to 10/90.
It would not be outside the scope of the invention to add mineral fillers (talc, CaCO3, Kaolin, etc), reinforcements (glass fibre, mineral fibre, carbon fibre, etc), stabilizers (heat stabilizers and UV stabilizers), fire retardants and colorants.
The compositions of the invention are prepared by the usual techniques for thermoplastics, such as, for example, extrusion or twin-screw mixers.